Engineering, design, and advisory company Aurecon supplied mechanical and Environmentally Sustainable Design (ESD) services for the iconic 144 Oxford Road office development in Rosebank, Johannesburg. This has played a key role in the project aiming for a 5-Star Green Star Design Certification from the Green Building Council of South Africa (GBCSA).
Developer Growthpoint Properties appointed Aurecon in 2017 for the 35 0000 m² premium-grade office development, completed at end 2019, which aims to capitalise on the demand for office space in the popular precinct.
Aurecon was part of the project team at an early stage while various iterations were reviewed in order to establish the most feasible scheme. Close collaboration with Paragon Group and the rest of the project team was necessary to ensure proper coordination of all building services. Aurecon is currently in the process of rebranding as Zutari, after officially announcing the separation of the African business from the Aurecon Group, effective from 1 January 2020.
The nine-storey development features two elongated office towers interlinked by a central atrium along the north-south axis. Spanning over the entire nine floors, the atrium offers a visual link to the outside. The west façades are shaped towards a curved glass pinnacle that cantilevers outwards towards the road.
The main façade consists of double-glazed unitised façades, incorporating a dark grey glass. The outermost façade of the northern building features a secondary offset glazed ‘skin’ with raking sides. The high-performance glazing used on the project had to be factored into the cooling load, according to Aurecon Technical Director Brandon Huddle (PrTech Eng, BBA). The glazing has been coated and baked especially with a variety of chemicals to reflect heat. This means that, while it allows natural light to enter, heat wavelengths are reflected back out of the building.
One of the key sustainability features of this project is the air-conditioning system based on four 800 kW CIAT chillers from Sky Shot Climate Solutions. The total cooling provided for is 3.2 MW, serving 17 air-handling units (AHUs) that cater for the different thermal zones in the building. Each AHU handles roughly 12 m3 to 18 m3 of air, which makes for a highly cost-effective design. The Variable Air Volume (VAV) diffusers used were provided by Rickard Air Diffusion. The diffuser groups each cover a 50 m2 to 100 m2 zone, and can each be controlled individually.
Each AHU is fitted with an intelligent control valve with a built-in energy meter, which means that the precise R/kWh can be calculated. The CIAT chillers have variable-speed condenser fans for increased energy-efficiency, supplying water at 6°C, which is returned from the building at 12°C.
A major contributor to the optimised energy performance of the building is the fact that the AHUs have dampers that are able to shut-off the return-air flow if the external ambient conditions is below that of the return-air temperature, which typically provides maximum benefit between 12°C to 18°C. This allows for natural cooling of the building, taking advantage of the ideal Johannesburg climate, especially in winter, spring, autumn, and cool summer mornings.
The building is actually very well sealed, as normally these unitised curtain wall façades tend to leak a lot. The air under economy cycle mode needs to be released from the building in order to allow supply air to enter. Relief air dampers on the roof in the atrium return-air path open and close automatically, depending on the economy cycle damper positions.
As long as the external temperature is lower than the temperature of the return-flow air, it means that the air-con system operates in economy mode. The entire HVAC system, in turn, is integrated with the Building Management System (BMS), which schedules the air-con system to operate from 05:00 to 19:00 as determined by the landlord.
The roof-level AHUs are covered in order to protect the ducting from solar-heat gain, which saves additional costs such as additional insulation and cladding. It also saves costs in that components such as the AHUs, control panels, and Variable Speed Drives (VSDs) do not have to be weather-proofed.
“If you add up all of these extra costs and the operational benefit, it is well worth the investment. An added benefit is that it facilitates any maintenance needed to be carried out by technicians,” Huddle points out. A particular innovation implemented by Aurecon on this project was to detect refrigerant leaks from the air-cooled chillers. This limits the environmental damage caused by refrigerants with ozone-depletion or global-warming potential.
Another ‘first’ for the project was using Siemens intelligent valves, which can be accessed by means of an app in order to determine energy consumption, flow rate, and valve positioning. In addition, there is BMS-addressable energy-efficient lighting throughout, water-saving sanitary fittings, a rainwater harvesting system, extensive glazing to maximise external views and natural lighting, and water-efficient landscaping.
A facilities manager was actively involved during the design phase to ensure that the operational intent of the sustainability initiatives was implemented effectively following the commissioning of the building services.
Described as an iconic development, 144 Oxford Road is surrounded by a leafy residential neighbourhood, while across the road there are trendy retail centres, hotels, and the Rosebank Gautrain Station. The Gautrain servitude cuts through the site, which restricted the allowable construction methodology to be used. Further to this, Oxford Road sits within the site boundary. All these factors contributed to a long and intensive design process that took into account site-specific parameters, together with stakeholders’ particular needs and requirements.
Aurecon worked closely with Growthpoint Properties, Paragon Group as architect, and the professional team through the various iterations of the building’s design to ensure that the mechanical services and the sustainability objectives were aligned seamlessly with the ultimate design.
“A visionary client, a strong professional team, and commitment to best sustainability practices led to a landmark development that will offer additional ‘green’ prime office space in Gauteng,” Aurecon Associate Yovka Raytcheva-Schaap concludes.